Genarray.create kind layout dimensions returns a new big array
whose element kind is determined by the parameter kind (one of
float32, float64, int8_signed, etc) and whose layout is
determined by the parameter layout (one of c_layout or
fortran_layout). The dimensions parameter is an array of
integers that indicate the size of the big array in each dimension.
The length of dimensions determines the number of dimensions
of the bigarray.

For instance, Genarray.create int32 c_layout [|4;6;8|]
returns a fresh big array of 32-bit integers, in C layout,
having three dimensions, the three dimensions being 4, 6 and 8
respectively.

Big arrays returned by Genarray.create are not initialized:
the initial values of array elements is unspecified.

Genarray.create raises Invalid_argument if the number of dimensions
is not in the range 1 to 16 inclusive, or if one of the dimensions
is negative.

Genarray.nth_dim a n returns the n-th dimension of the
big array a. The first dimension corresponds to n = 0;
the second dimension corresponds to n = 1; the last dimension,
to n = Genarray.num_dims a - 1.
Raise Invalid_argument if n is less than 0 or greater or equal than
Genarray.num_dims a.

Read an element of a generic big array.
Genarray.get a [|i1; ...; iN|] returns the element of a
whose coordinates are i1 in the first dimension, i2 in
the second dimension, ..., iN in the N-th dimension.

If a has C layout, the coordinates must be greater or equal than 0
and strictly less than the corresponding dimensions of a.
If a has Fortran layout, the coordinates must be greater or equal
than 1 and less or equal than the corresponding dimensions of a.
Raise Invalid_argument if the array a does not have exactly N
dimensions, or if the coordinates are outside the array bounds.

If N > 3, alternate syntax is provided: you can write
a.{i1, i2, ..., iN} instead of Genarray.get a [|i1; ...; iN|].
(The syntax a.{...} with one, two or three coordinates is
reserved for accessing one-, two- and three-dimensional arrays
as described below.)

Assign an element of a generic big array.
Genarray.set a [|i1; ...; iN|] v stores the value v in the
element of a whose coordinates are i1 in the first dimension,
i2 in the second dimension, ..., iN in the N-th dimension.

The array a must have exactly N dimensions, and all coordinates
must lie inside the array bounds, as described for Genarray.get;
otherwise, Invalid_argument is raised.

If N > 3, alternate syntax is provided: you can write
a.{i1, i2, ..., iN} <- v instead of
Genarray.set a [|i1; ...; iN|] v.
(The syntax a.{...} <- v with one, two or three coordinates is
reserved for updating one-, two- and three-dimensional arrays
as described below.)

Extract a sub-array of the given big array by restricting the
first (left-most) dimension. Genarray.sub_left a ofs len
returns a big array with the same number of dimensions as a,
and the same dimensions as a, except the first dimension,
which corresponds to the interval [ofs ... ofs + len - 1]
of the first dimension of a. No copying of elements is
involved: the sub-array and the original array share the same
storage space. In other terms, the element at coordinates
[|i1; ...; iN|] of the sub-array is identical to the
element at coordinates [|i1+ofs; ...; iN|] of the original
array a.

Genarray.sub_left applies only to big arrays in C layout.
Raise Invalid_argument if ofs and len do not designate
a valid sub-array of a, that is, if ofs < 0, or len < 0,
or ofs + len > Genarray.nth_dim a 0.

Extract a sub-array of the given big array by restricting the
last (right-most) dimension. Genarray.sub_right a ofs len
returns a big array with the same number of dimensions as a,
and the same dimensions as a, except the last dimension,
which corresponds to the interval [ofs ... ofs + len - 1]
of the last dimension of a. No copying of elements is
involved: the sub-array and the original array share the same
storage space. In other terms, the element at coordinates
[|i1; ...; iN|] of the sub-array is identical to the
element at coordinates [|i1; ...; iN+ofs|] of the original
array a.

Genarray.sub_right applies only to big arrays in Fortran layout.
Raise Invalid_argument if ofs and len do not designate
a valid sub-array of a, that is, if ofs < 1, or len < 0,
or ofs + len > Genarray.nth_dim a (Genarray.num_dims a - 1).

Extract a sub-array of lower dimension from the given big array
by fixing one or several of the first (left-most) coordinates.
Genarray.slice_left a [|i1; ... ; iM|] returns the 'slice'
of a obtained by setting the first M coordinates to
i1, ..., iM. If a has N dimensions, the slice has
dimension N - M, and the element at coordinates
[|j1; ...; j(N-M)|] in the slice is identical to the element
at coordinates [|i1; ...; iM; j1; ...; j(N-M)|] in the original
array a. No copying of elements is involved: the slice and
the original array share the same storage space.

Genarray.slice_left applies only to big arrays in C layout.
Raise Invalid_argument if M >= N, or if [|i1; ... ; iM|]
is outside the bounds of a.

Extract a sub-array of lower dimension from the given big array
by fixing one or several of the last (right-most) coordinates.
Genarray.slice_right a [|i1; ... ; iM|] returns the 'slice'
of a obtained by setting the last M coordinates to
i1, ..., iM. If a has N dimensions, the slice has
dimension N - M, and the element at coordinates
[|j1; ...; j(N-M)|] in the slice is identical to the element
at coordinates [|j1; ...; j(N-M); i1; ...; iM|] in the original
array a. No copying of elements is involved: the slice and
the original array share the same storage space.

Genarray.slice_right applies only to big arrays in Fortran layout.
Raise Invalid_argument if M >= N, or if [|i1; ... ; iM|]
is outside the bounds of a.

Copy all elements of a big array in another big array.
Genarray.blit src dst copies all elements of src into
dst. Both arrays src and dst must have the same number of
dimensions and equal dimensions. Copying a sub-array of src
to a sub-array of dst can be achieved by applying Genarray.blit
to sub-array or slices of src and dst.

Set all elements of a big array to a given value.
Genarray.fill a v stores the value v in all elements of
the big array a. Setting only some elements of a to v
can be achieved by applying Genarray.fill to a sub-array
or a slice of a.

Memory mapping of a file as a big array.
Genarray.map_file fd kind layout shared dims
returns a big array of kind kind, layout layout,
and dimensions as specified in dims. The data contained in
this big array are the contents of the file referred to by
the file descriptor fd (as opened previously with
Unix.openfile, for example). The optional pos parameter
is the byte offset in the file of the data being mapped;
it defaults to 0 (map from the beginning of the file).

If shared is true, all modifications performed on the array
are reflected in the file. This requires that fd be opened
with write permissions. If shared is false, modifications
performed on the array are done in memory only, using
copy-on-write of the modified pages; the underlying file is not
affected.

Genarray.map_file is much more efficient than reading
the whole file in a big array, modifying that big array,
and writing it afterwards.

To adjust automatically the dimensions of the big array to
the actual size of the file, the major dimension (that is,
the first dimension for an array with C layout, and the last
dimension for an array with Fortran layout) can be given as
-1. Genarray.map_file then determines the major dimension
from the size of the file. The file must contain an integral
number of sub-arrays as determined by the non-major dimensions,
otherwise Failure is raised.

If all dimensions of the big array are given, the file size is
matched against the size of the big array. If the file is larger
than the big array, only the initial portion of the file is
mapped to the big array. If the file is smaller than the big
array, the file is automatically grown to the size of the big array.
This requires write permissions on fd.

Array accesses are bounds-checked, but the bounds are determined by
the initial call to map_file. Therefore, you should make sure no
other process modifies the mapped file while you're accessing it,
or a SIGBUS signal may be raised. This happens, for instance, if the
file is shrinked.